KR102543614B1 - Offset cancellation circuit for operational amplifier - Google Patents

Abstract

An offset cancellation circuit that performs offset cancellation for an operational amplifier includes an operational amplifier and a feedback circuit that feeds back at least a portion of an output of the operational amplifier to an inverting input terminal of the operational amplifier, the feedback circuit comprising: A resistor located between an output terminal and a first node, a capacitor located between the first node and ground, a first switch located between an output terminal of the operational amplifier and the resistor, and a first switch located between the inverting input terminal and the first node and a second switch positioned between the first switch and the second switch, in a state where the first switch and the second switch are (ON), the voltage at the output terminal of the operational amplifier is fed back to the input terminal of the operational amplifier by the resistor and the capacitor. The offset cancellation is performed, and the offset cancellation is performed using a voltage stored in the capacitor in a state in which the first switch is turned off and the second switch is turned on.

Description

OFFSET CANCELLATION CIRCUIT FOR OPERATIONAL AMPLIFIER

The present invention relates to an offset cancellation circuit for canceling an offset for an operational amplifier.

In an actual operational amplifier, the output of the operational amplifier does not become 0 even when no signal is input to the input terminal, and the output of the operational amplifier at this time is called an offset.

1 shows a circuit comprising a plurality of operational amplifiers. Here, in the circuit of FIG. 1, the operational amplifier 101 is a low noise amplifier (LNA) with a gain of A ₁ , and the operational amplifiers 102, 103 and 104 have gains of A ₂ , A ₃ , and A , respectively. It may be a ₄ -in Programmable Gain Amplifier (PGA).

As shown in FIG. 1, in a circuit in which a plurality of operational amplifiers 101, 102, 103, and 104 are connected in multiple stages, a signal entering the input terminal of the operational amplifier 101 is amplified and transmitted to the output terminal of the operational amplifier 104. . At this time, the offset signal generated at the input terminal of the operational amplifier 101 is also amplified and displayed at the output terminal of the operational amplifier 104.

Specifically, when a signal does not enter the input terminal of the operational amplifier 101 (V _IN =0), the voltage (V ₄ ) of the output terminal of the operational amplifier 104 may be expressed as in Equation 1 below.

In Equation 1, V _OS1 is the offset voltage of the operational amplifier 101, V _OS2 is the offset voltage of the operational amplifier 102, V _OS3 is the offset voltage of the operational amplifier 103, and V _OS4 is the operational amplifier 104 ) may be an offset voltage of

As shown in Equation 1, the offset voltage (V _OS1 ) of the operational amplifier 101 is amplified by ((1+A ₁ )×A ₂ ×A ₃ ×A ₄ )) times at the output of the operational amplifier 104 appear.

Therefore, in a circuit in which a plurality of operational amplifiers are connected in multiple stages, unnecessary signal components such as an offset voltage at an input stage are excessively amplified and output.

In this regard, Korean Patent Registration No. 10-1783459 discloses a DC offset cancellation circuit.

The present invention is to solve the above-mentioned problems of the prior art, in an offset cancellation circuit for performing offset cancellation for an operational amplifier, by feeding back the voltage at the output terminal of the operational amplifier to the input terminal of the operational amplifier by means of a resistor and a capacitor. It is intended to provide a circuit that performs cancellation or performs offset cancellation using a voltage stored in a capacitor.

In addition, in an offset cancellation circuit for performing offset cancellation for a plurality of operational amplifiers, it is intended to provide a circuit for performing offset cancellation for any one of a plurality of operational amplifiers by means of a common resistor and a common capacitor.

However, the technical problem to be achieved by the present embodiment is not limited to the technical problems described above, and other technical problems may exist.

As a means for achieving the above-described technical problem, an embodiment of the present invention is an offset cancellation circuit for performing offset cancellation for an operational amplifier, wherein at least a part of an operational amplifier and an output of the operational amplifier is connected to the operational amplifier. A feedback circuit that feeds back to an inverting input terminal, wherein the feedback circuit includes a resistor located between an output terminal of the operational amplifier and a first node, a capacitor located between the first node and a ground, and the operational amplifier A first switch positioned between an output terminal and the resistor and a second switch positioned between the inverting input terminal and the first node, wherein the resistor and the capacitor are connected in an ON state of the first switch and the second switch. The offset is removed by feeding back the voltage of the output terminal of the operational amplifier to the input terminal of the operational amplifier, and in a state where the first switch is turned off and the second switch is turned on, using the voltage stored in the capacitor The offset removal may be performed.

In one embodiment, the voltage stored in the capacitor may be determined based on feedback in a state in which the first switch and the second switch are turned on.

In one embodiment, the output of the operational amplifier may not be fed back by turning off the first switch.

Another embodiment of the present invention is an offset cancellation circuit for performing offset cancellation on a plurality of operational amplifiers, comprising: a first operational amplifier, a second operational amplifier having an output of the first operational amplifier as an input, and the first operational amplifier; a feedback circuit for feeding back at least a portion of an output of the amplifier to an inverting input terminal of the first operational amplifier and feeding back at least a portion of an output of the second operational amplifier to an inverting input terminal of the second operational amplifier; A common resistance located between a first node connected to the output terminal of the first operational amplifier and the output terminal of the second operational amplifier and a second node connected to the inverting input terminals of the first and second operational amplifiers and the second node and A common capacitor positioned between grounds may be included.

In one embodiment, the feedback circuit may share the common resistance and the common capacitor, and perform offset cancellation for any one of the first and second operational amplifiers by the shared common resistance and common capacitor. .

In one embodiment, the feedback circuit includes a first switch positioned between an output terminal of the first operational amplifier and the first node, a second switch positioned between an inverting input terminal of the first operational amplifier and the second node, The method may further include a third switch positioned between an output terminal of the second operational amplifier and the first node, and a fourth switch positioned between an inverting input terminal of the second operational amplifier and the second node.

In one embodiment, in a state in which the first and second switches are turned on and the third and fourth switches are turned off, the output of the first operational amplifier is output by the common resistance and the common capacitor to the first operational amplifier. Offset is removed for the first operational amplifier by being fed back to the inverting input terminal of , and in a state where the first and second switches are turned off and the third and fourth switches are turned on, the common resistance and the common capacitor are As the output of the second operational amplifier is fed back to an inverting input terminal of the second operational amplifier, offset cancellation for the second operational amplifier may be performed.

In one embodiment, the feedback circuit may further include a first discrete capacitor connected to the inverting input of the first operational amplifier and a second discrete capacitor connected to the inverting input of the second operational amplifier.

In one embodiment, the feedback circuit is connected to the first individual capacitor in a state in which the first and second switches are turned off after the first and second switches are turned on and the third and fourth switches are turned off. Offset cancellation for the first operational amplifier may be performed using the stored voltage.

In one embodiment, the feedback circuit is connected to the second individual capacitor in a state in which the third and fourth switches are turned off after the first and second switches are turned off and the third and fourth switches are turned on. Offset cancellation for the second operational amplifier may be performed using the stored voltage.

The above-described means for solving the problems is only illustrative and should not be construed as limiting the present invention. In addition to the exemplary embodiments described above, there may be additional embodiments described in the drawings and detailed description.

According to any one of the above-described problem solving means of the present invention, in the offset cancellation circuit for performing offset cancellation for an operational amplifier, the offset is removed by feeding back the voltage at the output terminal of the operational amplifier to the input terminal of the operational amplifier by means of a resistor and a capacitor. Offset removal may be performed using a voltage stored in the capacitor.

Also, in the offset cancellation circuit for performing offset cancellation for a plurality of operational amplifiers, offset cancellation for any one of the plurality of operational amplifiers may be performed by a common resistor and a common capacitor.

In addition, it is possible to prevent generation of noise and unstable operation of the circuit due to feedback of unnecessary signals.

In addition, miniaturization of integrated circuits can be achieved.

The effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the description below.

1 shows a circuit comprising a plurality of operational amplifiers.
FIG. 2 shows a circuit for feeding back a voltage at an output terminal of an operational amplifier to an input terminal of the operational amplifier and a graph showing frequency characteristics of the circuit.
3 shows simulation results of frequency characteristics according to the presence or absence of offset cancellation.
4 shows a circuit that feeds back the voltage of the output terminal of the operational amplifier to the input terminal of the operational amplifier and simulation results of frequency characteristics of this circuit.
5 is an exemplary diagram of an offset cancellation circuit that performs offset cancellation for an operational amplifier in accordance with one embodiment of the present invention.
6 is an exemplary diagram of an offset cancellation circuit that performs offset cancellation for a plurality of operational amplifiers according to one embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily practice the present invention with reference to the accompanying drawings. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein. And in order to clearly explain the present invention in the drawings, parts irrelevant to the description are omitted, and similar reference numerals are attached to similar parts throughout the specification.

Throughout the specification, when a part is said to be "connected" to another part, this includes not only the case where it is "directly connected" but also the case where it is "electrically connected" with another element interposed therebetween. . In addition, when a part "includes" a certain component, this means that it may further include other components, not excluding other components, unless otherwise stated, and one or more other characteristics. However, it should be understood that it does not preclude the possibility of existence or addition of numbers, steps, operations, components, parts, or combinations thereof.

Terminology used herein is for describing the embodiments and is not intended to limit the present invention. In this specification, singular forms also include plural forms unless specifically stated otherwise in a phrase. As used herein, "comprises" and/or "comprising" does not exclude the presence or addition of one or more other elements other than the recited elements. Like reference numerals throughout the specification refer to like elements, and “and/or” includes each and every combination of one or more of the recited elements. In addition, expressions such as “first,” “second,” and the like used in this specification may modify various components regardless of order and/or importance, and to distinguish one component from another. It is used but does not limit the corresponding components and does not necessarily mean other components. For example, 'first resistance' and 'second resistance' may mean the same resistance or different resistances.

According to one embodiment of the present invention, as one of the methods for performing offset cancellation for an operational amplifier, a feedback circuit for feeding back a voltage at an output terminal of the operational amplifier to an input terminal of the operational amplifier may be connected.

2(a) shows a circuit for feeding back the voltage of the output terminal of the operational amplifier to the input terminal of the operational amplifier. FIG. 2(b) is a graph showing frequency characteristics of the circuit shown in FIG. 2(a).

Referring to (a) of FIG. 2, the resistor R and the capacitor C of the feedback circuit operate as a high pass filter (HPF).

Referring to (b) of FIG. 2 , the low frequency signal of the input signal is filtered by the high pass filter and then output. In this way, by feeding back the voltage of the output terminal of the operational amplifier to the input terminal, it is possible to prevent the DC offset signal from being amplified.

3 shows simulation results of frequency characteristics according to the presence or absence of offset cancellation.

Figure 3 (a) shows the case where the gain of the operational amplifier is 32 dB and offset cancellation is performed, and Figure 3 (b) is the simulation result of the frequency characteristics when the operational amplifier with the same gain does not perform offset cancellation am.

Comparing and referring to the results of (a) and (b) of FIG. 3 , by performing offset removal, the gain can be reduced in a low frequency band and the gain in other bands can be maintained.

FIG. 3(d) is a case where the gain of the operational amplifier is 0 dB and offset cancellation is performed, and FIG. 3(c) is a simulation result of frequency characteristics when offset cancellation is not performed. Comparing and referring to the results of (c) and (d) of FIG. 3, by performing the offset removal as described above, the gain in the low frequency band can be reduced and the gain in other bands can be maintained.

4 shows a circuit that feeds back the voltage of the output terminal of the operational amplifier to the input terminal of the operational amplifier and simulation results of frequency characteristics of this circuit.

4(a) shows a circuit in which operational amplifiers 401, 402, 403, and 404 are connected in multiple stages. For example, the operational amplifier 401 may be a low noise amplifier having a gain of A ₁ , and the operational amplifiers 402 , 403 and 404 may be programmable gain amplifiers having gains of A ₂ , A ₃ , and A _{4 ,} respectively.

When a signal is not input to the input terminal of the operational amplifier 401 (V _IN =0), the voltage of the output terminal of each operational amplifier 401, 402, 403, 404 is, for example, Equation 2 to Equation 2 below. 5 may appear.

In Equation 2, V ₁ is the voltage of the output terminal of the operational amplifier 401, A ₁ is the gain of the operational amplifier 401, and V _OS1 may be the offset voltage of the operational amplifier 401.

In Equation 3, V ₂ is the voltage of the output terminal of the operational amplifier 402, A ₂ is the gain of the operational amplifier 402, and V _OS2 may be the offset voltage of the operational amplifier 402.

In Equation 4, V ₃ is the voltage of the output terminal of the operational amplifier 403, A ₃ is the gain of the operational amplifier 403, and V _OS3 may be an offset voltage of the operational amplifier 403.

In Equation 5, V ₄ is the voltage of the output terminal of the operational amplifier 404, A ₄ is the gain of the operational amplifier 404, and V _OS4 may be an offset voltage of the operational amplifier 404.

(b) and (c) of FIG. 4 show simulation results of the frequency characteristics of the circuits 402 and 403 shown in (a) of FIG. Referring to (b) and (c) of FIG. 4 , it can be seen that the gain is reduced in a low frequency band and the preset gain is maintained in other bands.

Therefore, by feeding back the voltage of the output terminal of the operational amplifier to the input terminal of the operational amplifier as in the circuit shown in FIG.

However, when there is a signal input to the input terminal of the operational amplifier, a component caused by an input signal as well as a component due to an offset voltage among output voltages of the operational amplifier may be fed back to the input terminal of the operational amplifier. Due to this, there is a problem in that the output of the circuit becomes unstable and noise is generated.

In order to solve the above-described problems, the present invention intends to provide a method for implementing an offset cancellation circuit capable of controlling whether or not a voltage of an output stage of an operational amplifier is fed back by turning a switch OFF or ON.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

5 is an exemplary diagram of an offset cancellation circuit that performs offset cancellation for an operational amplifier in accordance with one embodiment of the present invention. 5 shows an offset cancellation circuit 500 in which four operational amplifiers 501, 502, 503 and 504 are connected in multiple stages. For example, operational amplifier 501 may be a low noise amplifier, and operational amplifiers 502, 503 and 504 may be programmable gain amplifiers.

Referring to FIG. 5 , the offset cancellation circuit 500 may include an operational amplifier 502 and a feedback circuit 510 connected to input terminals and output terminals of the operational amplifier 502 .

The feedback circuit 510 may feed back at least a portion of the output of the operational amplifier 502 to an inverting input terminal of the operational amplifier 502 . The feedback circuit 510 may include a resistor 511, a capacitor 512 and one or more switches.

For example, the resistor 511 of the feedback circuit 510 may be located between the output terminal of the operational amplifier 502 and the node 5a, and the capacitor 512 may be located between the node 5a and the ground. there is.

The feedback circuit 510 may include a switch 513 and a switch 514 . The switch 513 may be located between the output terminal of the operational amplifier 502 and the resistor 511, and the switch 514 may be located between the inverting input terminal of the operational amplifier 502 and the node 5a.

In the first mode before an AC signal is input to the operational amplifier 502, a common mode voltage, which is a DC voltage, may be input to the operational amplifier 502. At this time, the feedback circuit 510 converts the voltage of the output terminal of the operational amplifier 502 by the resistor 511 and the capacitor 512, for example, in a state in which the switches 513 and 514 are turned on to the operational amplifier. Offset cancellation can be performed by feeding back to the input of 502. At the same time, the capacitor 512 may be charged by the common mode voltage. For example, the voltage stored in the capacitor 512 may be determined based on feedback when the switches 513 and 514 are turned on.

The switch 513 may be turned OFF before the second mode in which the capacitor 512 is sufficiently charged and an AC signal is input to the operational amplifier 502 .

That is, in the first mode, the switches 513 and 514 of the feedback circuit 510 are turned on, and in the second mode, the switch 513 is turned off and the switch 514 is turned on.

In the second mode, the feedback circuit 510 may perform offset removal using the voltage stored in the capacitor 512 in a state where the switch 513 is turned off and the switch 514 is turned on, for example.

At this time, the output of the operational amplifier 502 may not be fed back by turning off the switch 513. That is, in the state in which the switch 513 is OFF, since the voltage at the output terminal of the operational amplifier 502 is not fed back to the input terminal of the operational amplifier 502, offset cancellation based on the components of the input signal of the operational amplifier 502 is not performed. Instead, offset cancellation may be performed based on the voltage stored in the capacitor 512 .

Accordingly, by turning off the switch 513 of the feedback circuit 510 and removing the offset using the voltage stored in the capacitor 512, it is possible to prevent the input signal component from being fed back unnecessarily.

Continuing to refer to FIG. 5 , the offset cancellation circuit may further include an operational amplifier 503 and a feedback circuit 520 connected to input terminals and output terminals of the operational amplifier 503 .

For example, the feedback circuit 520 includes a resistor 521 located between the output terminal of the operational amplifier 503 and the node 5b, a capacitor 522 located between the node 5b and the ground, and an operational amplifier ( A switch 523 located between the output terminal of 503 and the resistor 521 and a switch 524 located between the inverting input terminal of the operational amplifier 503 and the node 5b may be included.

As described above for the feedback circuit 510, in the first mode, the feedback circuit 520 operates as an operational amplifier by means of the resistor 521 and the capacitor 522 while the switches 523 and 524 are turned on. Offset cancellation can be performed by feeding back the voltage at the output of 503 to the input of the operational amplifier 503. At this time, the capacitor 522 may be charged by the common mode voltage.

Also, in the second mode, the feedback circuit 520 may perform offset removal using the voltage stored in the capacitor 522 while the switch 523 is turned off and the switch 524 is turned on.

The offset cancellation circuit shown in FIG. 5 can individually perform offset cancellation for each operational amplifier by connecting a feedback circuit to each operational amplifier. Therefore, in order to perform offset cancellation for a circuit including a plurality of operational amplifiers, a resistor and a capacitor corresponding to each operational amplifier must be included.

Since the pole and zero point of the gain are determined by the resistor and capacitor included in the feedback circuit, it is generally necessary to use a resistor and capacitor having a large value in order to perform offset cancellation for the operational amplifier.

Hereinafter, as an example, an offset cancellation circuit that can be miniaturized by sharing resistors and capacitors between a plurality of operational amplifiers will be described.

6 is an exemplary diagram of an offset cancellation circuit that performs offset cancellation for a plurality of operational amplifiers according to one embodiment of the present invention. 6 shows an offset cancellation circuit 600 in which four operational amplifiers 601, 602, 603 and 604 are connected in multiple stages. For example, operational amplifier 601 may be a low noise amplifier, and operational amplifiers 602, 603 and 604 may be programmable gain amplifiers.

Referring to FIG. 6 , an offset cancellation circuit 600 may include an operational amplifier 602 , an operational amplifier 603 and a feedback circuit 610 . The operational amplifier 603 may receive the output of the operational amplifier 602 as an input.

The feedback circuit 610 may feed back at least a portion of the output of the operational amplifier 602 to an inverting input terminal of the operational amplifier 602 . Also, the feedback circuit 610 may feed back at least a portion of the output of the operational amplifier 603 to an inverting input terminal of the operational amplifier 603 .

Feedback circuit 610 may include one or more resistors, one or more capacitors, and one or more switches. For example, the feedback circuit 610 may include a common resistor 611 , a common capacitor 612 , and switches 613 , 614 , 615 , and 616 .

The common resistor 611 is a node 6a connected to the output terminal of the operational amplifier 602 and the output terminal of the operational amplifier 603 and a node 6b connected to the inverting input terminal of the operational amplifier 602 and the inverting input terminal of the operational amplifier 603. ) can be located between A common capacitor 612 may be located between node 6b and ground.

The switch 613 may be located between the output terminal of the operational amplifier 602 and the node 6a. Switch 614 may be located between the inverting input of operational amplifier 602 and node 6b. The switch 615 may be located between the output terminal of the operational amplifier 603 and the node 6a. Switch 616 may be located between the inverting input of operational amplifier 603 and node 6b.

The feedback circuit 610 may further include one or more separate capacitors 617 and 618. Separate capacitors 617 and 618 may be connected to the inverting inputs of the respective operational amplifiers 602 and 603. For example, discrete capacitor 617 can be connected to the inverting input of operational amplifier 602 and discrete capacitor 618 can be connected to the inverting input of operational amplifier 603.

Unlike the offset cancellation circuit 500 of FIG. 5 , in the offset cancellation circuit 600 of FIG. 6 , the operational amplifier 602 and the operational amplifier 603 may share a common resistor 611 and a common capacitor 612 . Offset cancellation for either of the operational amplifiers 602 and 603 can be performed by the shared common resistor 611 and common capacitor 612 .

In the first mode before AC signals are input to the operational amplifiers 602 and 603, common mode voltages, which are DC voltages, may be input to the operational amplifiers 602 and 603.

In the first mode, the feedback circuit 610 operates on the operational amplifier 602 by the common resistor 611 and the common capacitor 612 in a state where the switches 613 and 614 are turned on and the switches 615 and 616 are turned off. Offset cancellation for operational amplifier 602 may be performed by feeding the output back to the inverting input of operational amplifier 602.

The feedback circuit 610 outputs the output of the operational amplifier 603 by the common resistor 611 and the common capacitor 612 in a state where the switches 613 and 614 are OFF and the switches 615 and 616 are ON. Offset cancellation for operational amplifier 603 can be performed by feeding back to the inverting input of 603.

For example, the feedback circuit 510 has a common resistance in a state in which the switches 613 and 614 are turned on and the switches 615 and 616 are turned off in the first time period of the first mode. Offset cancellation can be performed by feeding back the voltage of the output terminal of the operational amplifier 602 to the input terminal of the operational amplifier 602 by means of 611 and the common capacitor 612 . At this time, since the switches 615 and 616 are turned off, the voltage at the output terminal of the operational amplifier 603 is not fed back. At the same time, an individual capacitor 617 can be charged by the common mode voltage.

In addition, in the feedback circuit 510, the switches 615 and 616 are turned on in the second time interval (eg, the time interval after the first time interval) of the first mode, and the switch 613 and the switch ( 614 is OFF, the offset can be removed by feeding back the voltage of the output terminal of the operational amplifier 603 to the input terminal of the operational amplifier 603 by the common resistor 611 and the common capacitor 612. At this time, since the switch 613 and the switch 614 are OFF, the voltage at the output terminal of the operational amplifier 602 is not fed back. At the same time, an individual capacitor 618 may be charged by the common mode voltage.

The switches 613, 614, 615, and 616 may be turned OFF before the second mode in which the individual capacitor 617 and the individual capacitor 618 are sufficiently charged and an AC signal is input to the operational amplifier 602. Offset cancellation for operational amplifier 602 and operational amplifier 603 may be performed by individual capacitor 617 and individual capacitor 618 in the second mode.

For example, in the second mode, the feedback circuit 610 may perform offset removal for the operational amplifier 602 using the voltage stored in the individual capacitor 617 while the switches 613 and 614 are turned off. there is.

In addition, the feedback circuit 610 may perform offset removal for the operational amplifier 603 using the voltage stored in the individual capacitor 618 while the switches 615 and 616 are turned off.

Unlike the common resistor 611 and the common capacitor 612 that determine the pole and zero points of the gain, the individual capacitors 617 and 618 are intended to store voltage and do not have to have large values.

Therefore, in the offset cancellation circuit 600 including a plurality of operational amplifiers, offset cancellation can be performed using a relatively small space by sharing the common resistance 611 and the common capacitor 612 having large values. . Through this, it is possible to promote miniaturization of the integrated circuit.

The above description of the present invention is for illustrative purposes, and those skilled in the art can understand that it can be easily modified into other specific forms without changing the technical spirit or essential features of the present invention. will be. Therefore, the embodiments described above should be understood as illustrative in all respects and not limiting. For example, each component described as a single type may be implemented in a distributed manner, and similarly, components described as distributed may be implemented in a combined form.

The scope of the present invention is indicated by the following claims rather than the detailed description above, and all changes or modifications derived from the meaning and scope of the claims and equivalent concepts should be construed as being included in the scope of the present invention. do.

500: Offset elimination circuit 600: Offset elimination circuit
510, 520: feedback circuit 610: feedback circuit
511: resistance 611: common resistance
512 capacitor 612 common capacitor
513, 514: switch 613, 614, 615, 616: switch
5a, 5b: node 6a, 6b: node
617, 618: separate capacitors

Claims (10)

An offset cancellation circuit for performing offset cancellation for an operational amplifier, comprising:
operational amplifier; and
A feedback circuit for feeding back at least a portion of the output of the operational amplifier to an inverting input terminal of the operational amplifier;
The feedback circuit,
a resistor positioned between an output terminal of the operational amplifier and a first node;
a capacitor positioned between the first node and ground;
a first switch positioned between an output terminal of the operational amplifier and the resistor; and
A second switch located between the inverting input terminal and the first node
including,
In a first mode in which a common mode voltage, which is a DC voltage, is input to the operational amplifier and before an AC signal is input, the operational amplifier is operated by the resistor and the capacitor in a state in which the first switch and the second switch are turned on. The offset removal is performed by feeding back the voltage of the output terminal of the operational amplifier to the input terminal of the operational amplifier.
The first switch is turned off before changing from the first mode to a second mode in which the AC signal is input to the operational amplifier;
The second mode is to perform the offset cancellation using the voltage stored in the capacitor in a state in which the first switch is turned off and the second switch is turned on.
According to claim 1,
The voltage stored in the capacitor is determined based on feedback in a state in which the first switch and the second switch are turned on, the offset cancellation circuit.
According to claim 1,
By turning off the first switch, the output of the operational amplifier is not fed back, the offset cancellation circuit.
An offset cancellation circuit for performing offset cancellation for a plurality of operational amplifiers,
a first operational amplifier;
a second operational amplifier receiving the output of the first operational amplifier as an input; and
A feedback circuit for feeding back at least a portion of the output of the first operational amplifier to an inverting input of the first operational amplifier and feeding back at least a portion of the output of the second operational amplifier to an inverting input of the second operational amplifier; ,
The feedback circuit,
a common resistor located between a first node connected to the output terminals of the first operational amplifier and the output terminals of the second operational amplifier and a second node connected to inverting input terminals of the first and second operational amplifiers; and
A common capacitor positioned between the second node and ground
Comprising, an offset cancellation circuit.
According to claim 4,
wherein the feedback circuit shares the common resistance and the common capacitor, and performs offset cancellation for any one of the first and second operational amplifiers by the shared common resistance and common capacitor.
According to claim 4,
The feedback circuit is
a first switch positioned between an output terminal of the first operational amplifier and the first node;
a second switch positioned between an inverting input terminal of the first operational amplifier and the second node;
a third switch positioned between an output terminal of the second operational amplifier and the first node; and
A fourth switch located between the inverting input terminal of the second operational amplifier and the second node
Which further comprises, the offset removal circuit.
According to claim 6,
In a state where the first and second switches are turned on and the third and fourth switches are turned off, the output of the first operational amplifier is inverted by the common resistance and the common capacitor. Offset cancellation for the first operational amplifier is performed by being fed back to an input terminal;
In a state in which the first and second switches are turned off and the third and fourth switches are turned on, the output of the second operational amplifier is inverted by the common resistance and the common capacitor. The offset cancellation circuit for performing offset cancellation for the second operational amplifier by being fed back to an input terminal.
According to claim 7,
The feedback circuit is
a first discrete capacitor connected to the inverting input of the first operational amplifier; and
A second individual capacitor connected to the inverting input of the second operational amplifier
Which further comprises, the offset removal circuit.
According to claim 8,
The feedback circuit is configured in a state in which the first and second switches are turned off after the first and second switches are turned on and the third and fourth switches are turned off, and the first and second switches are turned off. 1 performing offset cancellation for the first operational amplifier using a voltage stored in an individual capacitor.
According to claim 8,
In a state in which the third and fourth switches are turned off after the first and second switches are turned off and the third and fourth switches are turned on, the feedback circuit is configured to and performing offset cancellation for the second operational amplifier using a voltage stored in two separate capacitors.

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